Soft contact lenses are produced by a number of methods including cast molding, spin-casting, lathing and combinations of casting with lathing. Lenses made using spin-casting or cast molding have not generally required extensive polishing although the edges are sometimes polished on lenses made by these methods. For example, when spun-cast lenses are knife-edged as described in U.S. Pat. Nos. 3,832,920 and 3,896,688, it may be desirable to subsequently buff (i.e., polish) the lens edge. Lenses made by lathing techniques require polishing since lathing leaves the surface of the lens striated and unsuitable for use as a contact lens.
In general, the polish compositions used in the manufacture of soft contact lenses have not been publicly disclosed. However, polish compositions known to the applicants and in the art are based upon suspensions of abrasive agents in either silicone or petroleum oils. For instance, suspensions of abrasives in kerosene have been used in processes (as described in U.S. Pat. No. 4,555,372) involving spincasting of a lens blank followed by lathing of the posterior portion of the lens. Soft contact lens materials require polish compositions to be substantially water free since the contact lens materials themselves are polishable only in their unhydrated states. Because of this, soft contact lens polishes differ from other polishes.
Previously known polish compositions have many disadvantages: 1) work areas must be kept ventilated and the fumes from the polish must be collected, 2) the kerosene based polish must be removed from the lens by expensive cleaning procedures involving the use of chloro and fluorocarbons, and 3)the lenses do not release from the molds readily.